The present invention concerns a character printing device. This device, used particularly in the field of data processing under the name of belt printer, permits rapid printing of the results of problems solved by a data processing system.
It is known to construct a device in which an endless belt bearing matrices of characters arranged in successive identical series unrolls continuously in front of a line to be printed on a sheet so as to align all the characters with each possible printing position. These characters generally marked by their rank number on the belt, starting from a reference character to which is assigned the rank number zero, and are spaced regularly on the belt. Printing units are arranged facing the belt and are distributed regularly with a spacing different from that of the characters; they are marked by an order number. In the case of a printer, these printing units of an electromechanical type control striking hammers. Such a device comprises a recording memory to record data concerning each character to be printed on a line; said data establish a relation between each character to be printed and its order number in the line to be printed. It further comprises a detection unit which, on one hand, can determine the position coincidences of the striking units and the characters, these coincidences appearing during the unrolling of the belt, and, on the other hand, mark by numbers the constant time intervals called scan periods and subscan periods, a scan being defined as the time separating two coincidences of a character with a predetermined striking unit, a subscan being defined as the time separating the successive groups of coincidences appearing in the course of a scan.
In this known type of printing device, a comparison system is connected to the outputs of the recording memory and to the outputs of the coincidence detection unit, so that in the course of the successive scans and subscans, the detection of identities between the output signals of the recording memory and the output signals of the detection unit causes, owing to the signals appearing at the outputs of this comparison unit, the manipulation of the striking units corresponding to these outputs through the agency of means for activating these striking units.
one of the disadvantages of this type of known device is the necessity for a comparison system in which a memory unit is connected to the read outputs of the recording memory through the intermediary of a coder which is also connected to a memory table containing data relating to the position of each character on the support belt, relative to a reference character. This table necessarily has large capacity since it must comprise as many cells as there are characters on the support belt. For that reason, a portion of the main memory of the data processing system is used for it. The large amount of data concerning the position of the characters on their support belt thus causes a large occupation of cells in the main memory and thereby decreases the utilization capacity of that memory for calculational data.